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Phenomenon and Treatment of Diesel Generator Partial Fault Part 1

Mar. 21, 2023

The starlight power generation equipment has carefully studied and analyzed the generator fault, and introduced the generator load, current and instrument fault analysis.

genset generator

Generator overload

1. Phenomenon:

1) The stator current indication exceeds the rated value;

2) The indication of active and reactive power meters exceeds the rated value.

2. Reason:

The stator or rotor of the generator may be overloaded for a short time in case of short circuit fault, generator out-of-step operation, group motor startup and forced excitation of the system.

3. Treatment method:

1) In case of system fault, monitor that the temperature of each part of the generator does not exceed the limit, and the stator current is the rated value.

2) The system has no fault, the single machine is overloaded, and the system voltage is normal:

A. Reduce reactive power to reduce the stator current to within the rated value, but the power factor shall not exceed 0.95, and the stator voltage shall not be less than 0.95 times the rated voltage. Pay attention to the time it takes for the stator current to reach the allowable value. It is not allowed to exceed the specified value.

B. If the reduction of reactive power cannot meet the requirements, ask the shift supervisor to reduce the active power.

C. If AC excitation regulator channel fault causes stator overload, switch AC regulator to DC regulator for operation.

D. Strengthen the inspection of generator end, slip ring and commutator. If possible, strengthen cooling: reduce the inlet air temperature of the generator, and add oil pump and fan to the generator and transformer unit.

E. During overload operation, closely monitor the stator coil, the cold and hot air temperature before and after the air cooler, and the vibration swing of the unit, which shall not exceed the allowable value, and make detailed records.

Generator three-phase current unbalance

Three-phase current unbalance refers to that the three-phase current is different in amplitude or its phase difference is not 120 °, or both.

1. Phenomenon:

1) The three-phase current indication of the stator is not equal to each other, the three-phase current difference is large, and the negative sequence current indication value also increases.

2) When the unbalance exceeds the limit and exceeds the specified operation time, the negative sequence signal device will send the signal of "asymmetric overload of generator".

3) Cause vibration and heat of rotor.

2. Reason:

1) One phase of the generator set and its circuit is disconnected or one phase of the circuit breaker is in poor contact.

2) A transmission line is not in full phase operation.

3) The single-phase load of the system is too large: if there is a single-phase load with huge capacity.

4) The fault of stator ammeter or meter circuit will also make the indication of stator three-phase ammeter asymmetric.

3. Treatment method:

When the three-phase current unbalance of the generator runs beyond the limit, if it is determined that it is not caused by the meter circuit fault, the load of the unit shall be reduced immediately to make the unbalance current lower than the allowable value, and then report to the system dispatcher. After the three-phase current is balanced, increase the unit load according to the dispatching order. The difference of the three-phase current of the hydro-generator shall not exceed 20% of the rated current, and the current of any phase shall not exceed its rated value. The allowable negative sequence current of the hydro-generator shall not exceed 12% of the rated current.

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